1. Field of the Invention
The present invention relates to a magnetic head comprising a magnetic pole layer capable of perpendicular recording, and a magnetic recording/reproducing system comprising that magnetic head, a recording medium, and a drive unit adapted to rotationally drive that recording medium in a constant direction and make that magnetic head movable in the radial direction of the recording medium.
2. Explanation of the Prior Art
In association with an increase in the areal recording densities of recording media such as a hard disk (hereinafter called simply the “recording medium”), there are now growing demands on improvements in the performance of a thin-film magnetic head mounted on a magnetic recording system such as a hard disk drive.
By the recording, for instance, such a thin-film magnetic head is broken down into a areal recording with the direction of a signal magnetic field aligned with the longitudinal direction of a recording medium and a perpendicular recording with the direction of a signal magnetic field in alignment with the direction orthogonal to the surface of a magnetic medium.
As of now, the areal recording is still prevailing; however, it will be superceded just about surely by the perpendicular recording in consideration of market trends toward increases in the areal recording densities of recording media. The perpendicular recording has the merit of an already recorded medium being less affected by thermal fluctuation, let alone the ability to make sure high recording densities.
Typically, the thin-film magnetic head of the perpendicular recording is built up of a thin-film coil adapted to generate a recording magnetic flux, and a main magnetic pole layer that extends rearward from the air bearing surface and is adapted to magnetize a recording medium on the basis of a recording magnetic flux generated at the thin-film coil. With such a thin-film head of the perpendicular recording, magnetic information is recorded on that recording medium, because the data tracks of the recording medium are magnetized under a perpendicular magnetic field generated at the main magnetic pole.
For the thin-film magnetic head of the perpendicular recording, there is a thin-film magnetic head known, which comprises a main magnetic pole layer located in such a way as to extend in a direction orthogonal to the air bearing surface, as noted above. Such a thin-film magnetic head of the perpendicular recording is generally called the “mono-pole type thin-film magnetic head”.
There is a specific structure of this mono-pole type thin-film magnetic head known (from Patent Publications 1, 2, 3, 4, etc.), in which, for instance, an auxiliary magnetic pole layer for receiving an auxiliary magnetic flux is coupled to a main magnetic pole layer for the purpose of increasing the strength of a perpendicular magnetic field thereby improving the overwrite performance. With the mono-pole type thin-film magnetic head, however, there would be some limits to improvements in the overwrite performance, as noted above.
With a thin-film magnetic head of the perpendicular recording proposed recently in the art, therefore, a write shield layer for reducing the spread of a magnetic flux released off a main magnetic pole layer is used in combination with the main magnetic pole layer that extends in the direction orthogonal to the air bearing surface as mentioned above for the purpose of, for instance, keeping the recording track width back from growing wide and making a magnetic flux gradient steep, thereby enhancing the recording density of the recording medium.
Such a type of thin-film magnetic head of the perpendicular magnetic mode is generally referred to as the “shield type thin-film magnetic head”. The write shield layer is spaced away from the main magnetic pole via a gap of up to 0.2 μm, and extends rearward from the air bearing surface, so that it is isolated from a main magnetic pole layer via a gap layer on a side near the air bearing surface and coupled to the main magnetic pole layer via a back gap on a side far away from the air bearing surface.
The shield type thin-film magnetic head comprising such a write shield layer makes sure improvements in the recording density of the recording medium, because the magnetic flux released off the main magnetic pole is so constricted that the gradient of the perpendicular magnetic field becomes steep.
And now, in order for the thin-film magnetic head of the perpendicular recording to have ever higher reliability, it must make sure stable magnetic operation regardless of whether it is of the shield type comprising the so-called shield or of the type comprising an auxiliary magnetic pole. With a conventional thin-film magnetic head, however, as there is an unwanted magnetic field (floating external magnetic field) generated from an external magnetic field-generation source such as a voice coil motor, it offers a problem that at a non-recording time, i.e., in a state with no recording current fed to the thin-film coil, unexpected writing (overwriting) takes place and information recorded on the recording medium is unintentionally erased off, although depending on the influences of that floating external magnetic field. Furthermore, recent rapid progresses of various media techniques render it impossible to factor out external magnetic fields other than those from the drives of magnetic recording/reproducing systems. Even in the state of the art, there is a growing risk of receiving external magnetic fields from music players (e.g., ipod (registered trade mark)) or hard disks mounted on cellular phones or the like.
With a perpendicular recording medium in particular, there is an unintentional writing problem, because due to the presence of a so-called lining layer located on the lower portion of a recording layer, an external magnetic field, if applied to it, causes a magnetic field to focus on the edge portion of the shield layer and then be absorbed in the lining layer. Providing a solution to that problem requires an all-out innovation with just only the structure of the magnetic head but also the whole magnetic recording/reproducing system taken into consideration.
The situation being like this, the present invention has for its object the provision of a magnetic recording/reproducing system and a thin-film magnetic head, in which the already written signals are kept back from degradation upon application of an external magnetic field.